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Prof. John S.O. Evans

Research Interests

My principal research interests lie in the field of solid state chemistry and involve the synthesis, characterisation and evaluation of new materials of potential industrial and academic interest. The technological impact of solid state chemistry over the last few decades has been immense, and has affected almost every aspect of our daily lives. Examples include the zeolite catalysts used in the petroleum industry, the magnetic materials used for data storage in modern computers, and the high temperature superconductors which have the potential to revolutionise a large number of technologies.

Recent areas of research (some of which are described in more detail below) include negative thermal expansion materials - materials that actually contract in volume when heated, new oxychalcogenide layered intergrowths, new chalcogenide materials, intercalation chemistry, the synthesis, properties and applications of magnetic nanoparticles and new ternary bismuth-containing oxides. These projects all contain elements of synthesis and characterisation and research students could expect to receive training in X-ray and neutron diffraction techniques, conductivity measurements, magnetic measurements and solid state NMR.

One of the major techniques for studying materials is powder diffraction. The group has state of the art powder diffractometers capable of measuring samples from 10 to 1500 K. These are used to follow the progress of reactions as a function of temperature and time, giving valuable insight into chemical processes and mechanistic pathways in the solid state. We are also interested in structure solution/refinement from powder data and several of the most complex structure solutions performed to date have come from our group. We are active in the development of methods for structural analysis, such as "surface fitting" of powder diffraction data and "distortion mode" analysis (with collaborators at Brigham Young) for understanding phase transitions and magnetic structures. We work closely with Alan Coelho on developing the topas academic software suite for powder diffraction. We also collaborate with colleagues at central facilities on techniques such as total scattering (the PDF method) for understanding correlated motion in materials and to probe the short range structure of amorphous materials. We have excellent in-house synthesis and characterization facilities including a new Quantum Design SQUID magnetometer and Physical Properties Measurement System. We work with others in Durham and elsewhere on single crystal diffraction, solid state NMR, neutron diffraction and conductivity measurements. The combination of facilities and expertise available make Durham a wonderful place to perform solid state research.

Negative Thermal Expansion and Framework Materials

A major area of interest is in the field of negative thermal expansion (NTE) - that is materials which contract when heated. Cubic zirconium tungstate, for example, contracts continuously over a previously unprecedented temperature range of 2 to 1050K. Such materials have a range of potential applications. In addition to its negative thermal expansion, ZrW2O8 exhibits oxide ion mobility at 450 K and unusual behaviour under applied pressure. Related materials such as ZrWMoO8 and ZrMo2O8 show oxygen migration at temperatures as low as 200 K.

We have been active in understanding both the synthetic routes to these materials and why they show such interesting behaviour. This property is not restricted to oxide materials and we've recently described "colossal" contraction in the framework cyanide Ag3[Co(CN)6] with colleagues from Cambridge and ISIS.

New Oxychalcogenides and Chalcogenides

Whilst there has been considerable research into both oxide and chalcogenide phases, relative little is known about materials containing simultaneously both oxide and chalcogenide anions. Interest in this area has grown enormously in recent years due to the discovery of superconductivity at remarkably high temperatures in systems such as LaOFeAs and FeSe. We have prepared a number of new, oxychalcogenides such as Bi2YO4Cu2Se2, with interesting magnetic and conduction properties.

Left: key structures involved in the synthetic pathway to ZrMo2O8 - a material that actually contracts in volume on heating. Right: the structure of the oxychalcogenide Bi2YO4Cu2Se2

"Structural and Mechanistic Studies of the Dehydration of MoO2PO3OH.H2O and the In situ Identification of Two New Molybdenum Phosphates", S.E. Lister, V.J. Rixom, and J.S.O. Evans, Chemistry of Materials, 22, 2010, 5279-5289.